(i) Technical Field
The present invention relates to a living-body information measuring device and a light-emitting element.
(ii) Related Art
Examples of a known technology for measuring living-body information include a photoplethysmographic sensor that measures a photoplethysmogram by using absorption of light by hemoglobin, and an oxygen saturation sensor that measures oxygen saturation by using dual-wavelength photoplethysmography. In recent years, blood flow sensors that detect blood flow information by using a Doppler shift of light caused by the velocity of red blood cells have been developed. Using advanced manufacturing technologies, the sizes of such blood flow sensors have been reduced so as to be attachable to a fingertip. The blood flow sensors are capable of measuring blood flow information, such as a blood flow, a blood velocity, and a blood volume.
Until recently, a single sensor device was used to measure a single type of living-body information. Recently, however, wearable devices that are each capable of measuring plural types of living-body information have been actively developed. In order to develop wearable devices that are capable of measuring plural types of living-body information, it is necessary to reduce the size and the cost of a sensor.
When simultaneously measuring the photoplethysmograph (or oxygen saturation) and blood flow information of a living body by irradiating the living body with light, it is necessary to use a single-mode laser beam, which has a narrower light-emission-spectrum width, to measure the blood flow information. However, the light-emission amount of a single-mode laser beam is small. On the other hand, it is necessary to use a light beam having a large light-emission amount to measure the photoplethysmogram (or oxygen saturation). Therefore, if a single-mode laser beam is used, the light-emission amount may be insufficient. Moreover, if a single-mode laser beam is used, the Doppler shift may generate noise.